This invention relates to a position control for a solenoid actuated valve, and more particularly to a control including a model-based feed-forward control component.
Solenoid actuated position control valves are used in a variety of automotive control applications, including exhaust gas recirculation for an internal combustion engine. The solenoid coil is typically energized with a fixed supply voltage that is pulse-width-modulated (PWM) to produce a desired coil current. The control may be either open-loop or closed-loop depending on the performance requirements of the particular application. Open-loop controls generally rely on empirically derived tables of commanded valve position vs. PWM duty cycle or coil current, while closed-loop controls utilize position feedback to adjust the PWM duty cycle or desired current based on a computed deviation of the detected valve position from the commanded valve position. Various combinations of open-loop and closed-loop controls have also been used.
While reasonably good results can be achieved with the above-described control techniques by carefully tailoring the various tables and control gains for a particular application, an extensive calibration effort is usually required, and the control particulars developed for one application are typically not readily usable in a different application. Accordingly, what is needed is a control that does not require extensive calibration effort, and that is capable of providing good position control performance in a variety of different applications.
The present invention is directed to an improved position control for a solenoid actuated valve. wherein the solenoid is activated based on the combination of a feed-forward component based on a model of the steady state operation of the valve and a closed-loop feedback component that responds to changes in the commanded position and compensates for any inaccuracy in the steady state model. The method involves a valve characterization procedure in which the actual force generated by the solenoid is measured for various combinations of valve position and solenoid current, resulting in a table of coil current in terms of developed force and valve position. In operation, the model is used to estimate the solenoid force required to achieve the commanded valve position under steady state operating conditions, and a controller addresses the table to obtain a feed-forward coil current command as a function of the commanded valve position and the estimated solenoid force. The feed-forward command is combined with a closed-loop feedback coil current command, which in turn, is used to develop a corresponding PWM duty cycle, given the solenoid temperature and the magnitude of the supply voltage.
Since the methodology of the present invention includes modeling the physical parameters of the valve, the resulting control is more precise than conventional controls that do not account for variations in the modeled parameters. Additionally, the calibration effort required for the control of the present invention is significantly reduced, and the modular nature of the control minimizes the re-design and re-calibration efforts occasioned by changes in overall system design.